/*
 * =============================================================================
 * Copyright by Benjamin Sempere,
 * All rights reserved.
 * =============================================================================
 * Author  : Benjamin Sempere
 * E-mail  : benjamin@sempere.org
 * Homepage: www.sempere.org
 * =============================================================================
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package org.sempere.commons.jpa;

import javax.persistence.EntityManager;
import javax.persistence.NoResultException;
import javax.persistence.Query;
import java.util.Collection;
import java.util.Map;

/**
 * Base class for any Data Access Object (DAO) built on JPA API.
 *
 * @author bsempere
 */
public abstract class AbstractDAO {

    private EntityManager entityManager;

    /**
     * Default class constructor
     */
    public AbstractDAO() {
    }

    /**
     * Constructor that takes the entityManager to be used
     *
     * @param entityManager the entityManager to be injectect
     */
    public AbstractDAO(EntityManager entityManager) {
        this.entityManager = entityManager;
    }

    /**
     * Returns the entity manager built around the given persistence unit name
     *
     * @return EntityManager
     */
    public EntityManager getEntityManager() {
        return this.entityManager;
    }

    // *************************************************************************
    //
    // Commons methods ...
    //
    // *************************************************************************

    protected <T> T find(Class<T> entityClass, Object entityPK) {
        T entity = this.getEntityManager().find(entityClass, entityPK);
        if (entity == null) {
            throw new NoResultException("Entity with class [" + entityClass + "] and  PK [" + entityPK + "] does not exist in the database.");
        }
        return entity;
    }

    protected <T> T findNullable(Class<T> entityClass, Object entityPK) {
        return this.getEntityManager().find(entityClass, entityPK);
    }

    protected <T> T persist(T entity) {
        this.getEntityManager().persist(entity);
        return entity;
    }

    protected <T> T merge(T entity) {
        this.getEntityManager().merge(entity);
        return entity;
    }

    protected <T> void remove(Class<T> entityClass, Object entityPK) {
        T entity = this.find(entityClass, entityPK);
        this.getEntityManager().remove(entity);
    }

    @SuppressWarnings("unchecked")
    protected <T> T getResultFromNamedQuery(String queryName) {
        return (T) this.getResultFromNamedQuery(queryName, null);
    }

    @SuppressWarnings("unchecked")
    protected <T> T getResultFromNamedQuery(String queryName, Map<String, Object> parameters) {
        Query query = this.getEntityManager().createNamedQuery(queryName);
        if (parameters != null) {
            for (String parameterName : parameters.keySet()) {
                query.setParameter(parameterName, parameters.get(parameterName));
            }
        }
        return (T) query.getSingleResult();
    }

    protected <T> Collection<T> getResultsFromNamedQuery(String queryName) {
        return this.getResultsFromNamedQuery(queryName, null);
    }

    @SuppressWarnings("unchecked")
    protected <T> Collection<T> getResultsFromNamedQuery(String queryName, Map<String, Object> parameters) {
        Query query = this.getEntityManager().createNamedQuery(queryName);
        if (parameters != null) {
            for (String parameterName : parameters.keySet()) {
                query.setParameter(parameterName, parameters.get(parameterName));
            }
        }
        return query.getResultList();
    }

    protected void setParameters(Query query, Map<String, Object> parameters) {
        if (parameters != null) {
            for (String parameterName : parameters.keySet()) {
                query.setParameter(parameterName, parameters.get(parameterName));
            }
        }
    }

    // ********************************************************************************
    //
    // Setter for dependencies injection
    //
    // ********************************************************************************

    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }
}
